Cheeky! My ATPL's were done in 2005. I'm a bit rusty!
I think my confusion is coming from looking at the FCOM. Between BAT1 and AC ESS BUS, I see the contactor, then a box with STAT INV in, then the AC ESS BUS. However, there's a box coming off between the last two, labelled the AC STAT INV (with the 9XP on top). Do the STAT INV and the AC STAT INV do the same thing, and if so, why are there two?